1. Field of the Invention
This invention relates generally to a secondary DC power source for a satellite system and, more particularly, to a technique for using secondary DC power from a frequency generator on a satellite to provide secondary DC power to a low noise amplifier/frequency downconverter and a satellite beacon assembly.
2. Discussion of the Related Art
Various communications systems, such as certain cellular telephone systems, cable television systems, Internet systems, military communications systems, etc., make use of satellites orbiting the Earth to transfer signals. A satellite uplink communications signal is transmitted to the satellite from one or more ground stations, and then re-transmitted by the satellite to another satellite or to the Earth as a downlink communications signal to cover a desirable reception area depending on the particular use. The uplink and downlink signals are typically transmitted at different frequencies, are polarized and are coded. For example, the uplink communications signal may be transmitted at 30 GHz and the downlink communications signal may be transmitted at 20 GHz.
The satellite includes a satellite structure or bus that provides primary DC power. System components within the satellite, referred to as the satellite payload, include electrical components and systems that operate on secondary DC power, having a lower voltage than the primary DC power. For example, the primary DC power may be 50V and the secondary DC power may be 6.5V.
The satellite payload includes an antenna system having a configuration of antenna arrays that receive the uplink signals and transmit the downlink signals to the Earth. The antenna, signals received by the antenna arrays on a particular antenna channel are typically switched to another channel to be included on a downlink signal for one of a plurality of transmission antennas directed to different locations.
FIG. 1 is a schematic block diagram of a signal switching architecture 10 that provides signal switching on a satellite. The signal architecture 10 is a general depiction of this type of a system on a satellite, and it is intended to be exemplary only. The signal architecture 10 includes a series of channels 12 connected to four separate receive antennas 16. Only one of the channels 12 will be discussed herein with the understanding that the other channels operate in the same manner. The channel 12 includes a waveguide input filter 14 that filters the received uplink signal to a bandwidth in which the desired signal is contained. The filtered signal from the antenna 16 is then sent to a low noise amplifier and frequency downconverter (LNA/DC) 18 where the signal is amplified and downconverted to a lower frequency suitable for the switching operation. The LNA/DC 18 receives a local oscillator (LO) signal from a frequency generator. The LNA/DC 18 includes redundant amplification and down converting components.
Each of the amplified and downconverted signals on each channel 12 is sent to a separate splitter 26 within an input multiplexer 28. Each splitter 26 includes four outputs. The multiplexer 28 also includes a switch 30 in each channel 12 that receives an input signal from each of the splitters 26 so that the switch 30 can select which of the antennas 16 is to be connected to that channel. Therefore, all of the uplink signals for the four separate antennas 16 can be switched to any one of the channels 12. The selected antenna""s 16 downconverted signal or intermediate frequency is applied to a second bandpass filter 32 where it is further filtered to remove additional noise and further limit the bandwidth. The bandwidth of the filters 32 are set to a narrow frequency band so that a particular frequency from any one of the antennas 16 can be provided on any one of the channels 12.
The multiplexer 28 further includes a plurality of transfer switches 34 that allow the signal on a particular channel 12 to be switched to another channel 12. A careful review of the switches 34 show how five channels are provided from four antennas 16. As is apparent, the center channel is a spare channel that is not connected to a bandpass filter 32, and thus is a redundant channel. By switching the transfer switches 34, the spare channel can be selectively connected to one of the two center channels in the multiplexer 28.
A signal on each channel from the multiplexer 28 is applied to a test coupler 38, and then to a channel amplifier (CAMP) 40 that provides both fixed gain and controlled gain for the signal. The signal from the amplifier 40 is then applied to a frequency upconverter (UC) 42 that frequency upconverts the downconverted frequency signal to the higher downlink frequency for transmission. The UC 42 also receives an LO signal from the frequency generator to provide the upconversion. The upconverted signal is then applied to a traveling wave tube (TWT) amplifier 44 that increases the power of the signal for transmission to the Earth. A power converter 46 receives primary satellite DC bus power (50V), and reduces the primary power to secondary DC power for each of the amplifier 40, the UC 42. It supplies a separate secondary DC voltage to the TWT amplifier 44.
The amplified signal from the TWT amplifier 44 is applied to a transfer switch 50 within an output multiplexer 52. The switches 50 receive the downlink signals from the five separate channels 12, and select the signals on these channels to be on one of the downlink channels. The signals from the switches 50 are applied to a switching network 54 that provides high power waveguide switching. The switched signals from the switching network 54 provide four separate signals where each signal from a particular downlink channel is applied to each of three switch selectors 56. Therefore, the switch selector 56 select one of the four channels to be output onto one of three separate downlink antennas 58.
A challenge in satellite design and assembly is to minimize cost, size, weight, power and integration complexity. One area in which design complexity, weight and cost can be reduced is by reducing the requirement for multiple secondary power converters. In the known signal architecture of the type disclosed in FIG. 1, the LNA/DCs 18 would operate on secondary DC power. Thus, a power converter would be required to convert the primary satellite bus DC power to the secondary DC power suitable for the LNA/DCs 18. A separate DC power converter could be provided for each one of the LNA/DCs 18, or a single DC power converter could be provided for all four of the LNA/DCs 18. Additionally, the amplifiers 40 and the UCs 42 also require secondary DC power that is provided in this example by the power converter 46.
Further, in known satellite payload architectures, a stand alone secondary DC power converter is sometimes used to provide secondary DC power to the satellite beacon assembly that provides a downlink beacon signal to the Earth for calibration purposes. In those systems where a stand alone converter was not used for this purpose, the beacon assembly included an internal secondary power converter. Thus, because secondary DC power converters are heavy and require significant satellite space and resources, the several such converters typically required in satellite payload designs added significant cost and weight to the satellite.
What is needed is a secondary DC power conversion scheme on a satellite that reduces the number of secondary DC power converters needed to reduce the cost, size, weight and integration complexity of a satellite payload. It is therefore an object of the present invention to provide such a technique.
In accordance with the teachings of the present invention, a technique for providing secondary DC power to certain satellite payload components is disclosed that reduces the number of secondary DC power converters heretofore required in the art. Particularly, a known frequency generator that provides local oscillator signals to the downconverters and Upconverters in the satellite payload is used as a source of secondary DC power, instead of providing a separate secondary power source for these components. Thus, a plurality of secondary DC power lines is tapped off of the frequency generator and applied to certain satellite payload components, such as the LNA/DCs and the upconverters. Additionally, the secondary DC power available from the frequency generator is used as a secondary DC power source for a satellite beacon assembly that provides a signal to a beacon antennal.